After you park & shut off, do you store your fob very close to your car? If the fob remains in range with the car, it keeps active for a longer period of time & will run the battery down more quickly. The pinhole red LED on your fob should flash slowly to indicate it's within range & using more power. This isn't a "go read the manual" response but there's several pages in the owner's manual chapter 2 about fob range, when it puts itself into power saving mode, how you can force it into power saving mode, how to wake it, etc. just in case yours is sleeping when you need it to be awake.

If you're carrying both fobs with you, maybe block one with a Faraday bag, Mentos tin or aluminum foil, just to eliminate a variable from your situation. Are both fobs behaving erratically like this? That would suggest the car not the fobs. Maybe it's one of those mysterious Subaru electronic things that just needs a power cycle (disconnect battery negative cable, press brake pedal, reconnect battery; be prepared to reset your auto windows).

FWIW my phone (ATT/TMobile) usually goes in the storage cubby before I even push the start button. One of the antennas is right above the cubby & it hasn't caused me any problems. Good luck.

 

Malfunctioning fobs that drain batteries have been reported before but that's about it AFAIK.

+1 for disconnecting the battery - it's also commonly suggested to remove both cables and briefly short them together to fully discharge the electrical system. I would also suggest not carrying both fobs, or (as suggested) shielding one of them, use them individually to see if the problem is related to one or the other.

 

Thanks for the replies. I typically keep the main fob in the car and the spare about 7 feet away. I never knew you weren't suppose to keep the key in the car. Was never an issue when the car was new as the batteries lasted years and I'd get a "Access key battery low" message instead of "Access key not detected". But I'm hoping the cheap battery + battery drain is the issue. My new Energizer batteries will be here Wednesday and I'll be sure to store the fobs over 2m from the car.

I'll read through the manual as well and tin foil one fob. The main reason for carrying 2 is in case one fails especially on road trips. But even with both keys in the car, I still see the message which makes me think it's not fob related.

If I'm still having issues after that I'll try disconnecting the battery. I've reset the auto windows before but the passenger window sometimes won't close all the way which is a bit of another issue.

Anyway, I'll report back when if it's still happening with the new batteries and storing the keys away from the vehicle. Since the issue is sporadic, it may take some time to determine if it was an actual fix.

 

Another thing to add that may make a bit of a difference. I recently replaced a battery in an apple AirTag and it wasn’t registering. Brand new Duracell 2032. Turns out, little kids like to swallow them? And that’s bad. So they’ve added a bitter coating to them to discourage kids from putting them in their mouth. My AirTag wouldn’t register the battery at all until I wiped the bottom of the battery off with an alcohol wipe. Sounds stupid. Wouldn’t have even thought to try it if I didn’t find it in an article online. And yes, I tried licking it. It is really bitter.

 

I believe the major problem you are describing (access key not detected) has nothing to do with the battery in the key Fob.

The battery is used to send a signal to the BIU (Body Integrated Unit) so that the BIU allows the doors to open. I suspect (but I do not know) that when this signal is sent it also sends a code that disables the security system (bypassing the requirement of RFID chip security) to allow the engine to start.

The RFID chip in the Fob (this chip does not use power from the Fob battery) is read by the antennae around the start button. The antennae reads and amplifies the signal and sends the signal to the BIU. The BIU then communicates with the ECU and allows the vehicle to start when the start button is pushed.

When the signal from the RFID chip cannot be detected by the antennae around the start button, placing the fob on the start button enhances the signal (due to proximity to the antennae) and allows the vehicle to start.

I suspect the actual problem you are having is RF (Radio Frequency) interference. If there is a signal in your area that is at a similar frequency to your vehicle it may be over powering the RFID and Fob communication with your vehicle.

My 2011 vehicle with a start button repeatedly had this problem in various locations.

Hope this all makes sense.

Seagrass

 

I believe the major problem you are describing (access key not detected) has nothing to do with the battery in the key Fob.

The battery is used to send a signal to the BIU (Body Integrated Unit) so that the BIU allows the doors to open. I suspect (but I do not know) that when this signal is sent it also sends a code that disables the security system (bypassing the requirement of RFID chip security) to allow the engine to start.

The RFID chip in the Fob (this chip does not use power from the Fob battery) is read by the antennae around the start button. The antennae reads and amplifies the signal and sends the signal to the BIU. The BIU then communicates with the ECU and allows the vehicle to start when the start button is pushed.

When the signal from the RFID chip cannot be detected by the antennae around the start button, placing the fob on the start button enhances the signal (due to proximity to the antennae) and allows the vehicle to start.

I suspect the actual problem you are having is RF (Radio Frequency) interference. If there is a signal in your area that is at a similar frequency to your vehicle it may be over powering the RFID and Fob communication with your vehicle.

My 2011 vehicle with a start button repeatedly had this problem in various locations.

Hope this all makes sense.

Seagrass

Seagrass makes a lot of sense. However I have had this issue occur at a trailhead in a remote area where there was no cell reception, although there were other cars parked in the lot. When the unlock button was pressed, it was not recognized and the lights would not flash. Repeatedly pushing buttons caused it to eventually work.

 

Thanks Seagrass. I too suspect it's something other than the fob, but figure it's easiest to troubleshoot the fob first.

The problem happens regardless of location - happened on a trip this weekend 150 miles away but I suppose it could be something in the car like my phone causing some interference. So will try #2 in my original post (keeping the key in the door pocket) and see if that still causes the issue. Seems unlikely as well, but I did read in another thread that it helped one person.

 

Possibly part of your issue - anytime I have my key in the same pocket as my cell phone I will get the "access key not detected" message. If I remove the key, or phone from the same location, it immediately works again. The order doesn't seem to matter, as in, the phone could be in front of the key or the key could be in front of the phone and the signal will be blocked and the key not detected. I have a Google Pixel 4a 5G but my wife can put the key buried in her purse with her iPhone 10 and never has the issue, so it seems it can be phone specific.

 

Well, since replacing the battery with an Energizer, storing the key fob in my house and placing the key in the inside door handle in the car (away from my phone) I've been 5 for 5 with starts and it's been unlocking the car just fine. Hopefully that is it, but we'll see how things go for the next month or so

 

Funny you say that, since moving my phone mount to the window air vent Iv starting getting the same message. My key is always in the top cubby in the door.

 

I suggest that anyone who gets this message really try changing the battery with a high quality CR2032 battery like one from Energizer. I tried every idea everyone on the blogs suggested but didn’t try the battery because both remotes were not working. After days of frustration and almost having it towed to the dealer for service I finally decided what the heck I’ll try a battery. Changed the battery in one, the remote magically worked the other remote still did not. Changed it’s battery and again magically it worked too. All they both needed was a newer stronger battery the old one was too weak to get the signal to the antennas I guess.

 

I’ve been having this same problem for about 4 months now with only one remote. I’ve changed the batteries twice using new Energizer batteries. Seems to work for a while then starts up again. Randomly occurs at home and all about town, so not an RF interference issue. Personally I just think it’s crapping electronics between the car and the FOB. Usually I can get it to work by locking the vehicle, while sitting in the car. Then it will start. Same goes when it won’t open the door via proximity. I then hit the lock and unlock in the FOB.

 

I'm having this issue with my 2016 Outback. I've checked battery and it is full strength. I do no carry the other FOB with me. I have taken FOB apart to check battery and make sure contacts are good, put it back together and it's good for a week or two and then back to driving me nuts. I do have after market starter so I think it's the electronics causing this. I have just become aware of putting FOB closest start button...hopefully this helps me. If I get stranded, I'll probably lose my mind.

 

Another possibility - from what I've read, certain aftermarket LED bulb replacements generate interference which can cause various electrical issues, including unpredictable keyless access behavior. If you've installed any LEDs just try going back to the original incandescent bulb(s) to see if the problem is resolved.

 

Same problem on my 2023 forester. Definitely a design fault. I think the radio interference is a likely explanation.

 

I've had this same issue for years on my 2018 Outback. Very perplexed because it's seemingly related to the key fobs going to sleep. I say this because the red LED should flash every time you press a button but oftentimes it won't. As soon as the key fob "wakes up" and starts responding to button presses, everything works great. Same issue with both keys and it doesn't get better with battery exchanges (the car will notify me when that's the issue).

 

I have this problem. I hate the push start buttons. I prefer a keyed ignition